The new channels in the Unlicensed National Information Infrastructure (UNII) band (5 GHz), shown in FIG. 1, require the support of new regulatory requirements such as dynamic frequency selection (DFS), transmit power control (TPC) and uniform spreading (US, or equal loading). While the original 802.11a and the subsequent 802.11n standards, developed for radio local area network (LAN) applications for packet-switched transmissions based on a time division duplex (TDD) operation with low channel occupancy, easily support these new regulatory requirements, such support is more difficult and challenging with simultaneously bi-directional (full duplex) circuit-switched wireless link applications with very low latency limits (i.e. <20 μsec).
One such wireless link over the UNII band is described in patent applications by Mohebbi, WO2005025078, filed Sep. 3, 2003 and WO2005069249, filed Jan. 12, 2004, both entitled “Short-Range Booster” and the contents of which are incorporated by reference herein for all purposes. These applications describe a booster system for frequency division duplex (FDD) cellular systems, as shown in FIG. 2, supporting FDD-type cellular systems according to a number of standards such as wideband code division multiple access (WCDMA), cdma2000 and global system for mobile (GSM), general packet radio system (GPRS) and the enhanced data GSM environment (EDGE).
In the short range booster system 200 shown in FIG. 2, Hop1 and Hop3 are substantially operating at the same frequency in the cellular band, while Hop2 is tuned to operate at the UNII band or the industrial, scientific and medical (ISM) band. Hop1 is the communication link to the base transceiver system (BTS), while Hop3 is the communications link to the mobile subscriber (MS) unit in FDD mode. Hop2 is the communications link between a network unit 202 and a user unit 204 of the short range booster system 200, which includes two-way traffic and control channels, required to meet the latency (delay) requirements of the target cellular system (e.g. WCDMA requires a latency of no more than 20 μsec for the total booster operation, so that a RAKE receiver, in the handset or BTS, can combine direct and boosted signal energies).
There are in total nearly twenty-three non-overlapping 20 MHz channels defined in the United States for the UNII spectrum shown in FIG. 1. Current WiFi systems such as 802.11 “a” or “n”, use one or two channels in this spectrum, operating in TDD mode for Radio LAN applications. These systems cannot meet the FDD requirements of cellular systems, with its required latency, while meeting the regulatory requirements for DFS, radar detection, and uniform spreading. For example, just the preamble and the “signal field” symbol of the 802.11a (or n) systems, which are required for the physical layer operation, can be 20 μsec. This alone consumes the allowed latency budget, leaving no margin for the other processing delays for the transceiver. Further, the 802.11 media access control (MAC) layer introduces non-deterministic latency, as the MAC operation is based on CSMA/CA.
The UNII band is divided into two distinct separate blocks with contiguous channels in each block, for FDD operation (an example is shown in FIG. 3). In such FDD partitioning, for example, the “Duplex I” block can have 7 channels, while “Duplex II” block can include 8 channels. Therefore, in the given example, a channel (or a number of channels) in the “Duplex I” band can be assigned for a given direction between the network unit and user units shown in FIG. 2, while transmissions in the other direction can be supported by a channel (or number of channels) in the “Duplex II” block. Although this arrangement will meet the FDD requirement of the cellular systems, it will not meet the DFS and Uniform Spreading requirements of UNII band, nor will it meet the short latency requirement of cellular systems.